This invention relates to a disposable hypodermic syringe, and more particularly to such a syringe which is maintained in a sterile condition without external packaging.
Louis Pasteur in his experiments relative to the behavior of bacteria fashioned glass flasks with various neck shapes. Each flask contained an enclosed sterial media. The necks on some flasks allowed airborne dust particles to fall on the contained media, which soon became contaminated as evidenced by the appearance of bacterial growth. The media in those flasks with S-curved necks, or which presented a "tortuous path" for airborne dust and bacteria, remained sterile. The dust and bacteria were stopped at the openings to the curved necks, as well as at the curves in the necks. Hypodermic injection devices using Pasteur's "tortuous path" principle have long been known, as may be seen by the "Monoject" brochure, copyright 1973, by Sherwood Medical Industries, Inc.
A sterilized hypodermic syringe assembly is seen in U.S. Pat. No. 2,860,635 to E. H. Wilburn which includes a double walled piston assembly. The piston has an externally threaded head end upon which a piston plug is screwed. Simple molding processes are precluded by thread formations. A needle cap is provided to cover the front end and the needle extending therefrom. The needle cap is press fitted onto the front of the Wilburn assembly. Conceivably, unless protected by external packaging, handling could cause Wilburn's double walled piston assembly to withdraw wholly or partially from the barrel, or the protective needle cap to loosen from the interference fit and fall off exposing the needle.
U.S. Pat. No. 3,485,239 discloses a sterile syringe utilizing two strips of removable gas permeable tape to hold a needle covering cap in place, and to retain a plunger within the syringe barrel. The tape performs a sieving effect, resisting the package of pathogenic organisms toward the interior of the syringe after sterilization.
A self-sealed hypodermic syringe is needed which will maintain sterility without airtight seals, and which is firmly held in the sterile configuration by means of a single breakable bond until ready for use.